i had some issues with php7.1, but i don't think it was the core that was causing issues but a theme or a plugin, so.... for the moment i'm sticking with 7.0 as it is a bit faster than 5.6. these conditions will vary, in short, depending on the plugins and themes you're using more than the core of SMF if you're running at least 2.0.14...

i wager your login issue has little to do with the version of php but more to do with the files. you may want to consider fresh 2.0.14 files and then upgrade to 2.0.15, abandoning all the themes and plugins until you can reinstall them one by one in hope to find your conflict(s).

"Before you allow people access to your forum, especially in an administrative position, you must be aware that that person can seriously damage your forum. Therefore, you should only allow people that you trust, implicitly, to have such access." -Douglas

I have uploaded a fresh set of files. Still no possibillity to login. Then I downloaded the 2.0.15 upgrade package and uploadede that. I ran the upgrade.php, which I could do with my admin user account and password, but I still can't log in. A little improvement har occured though Now I don't get a white screen, bit I get this message in stead, no matter which user I try to log in with.

But that line is allready there. In the Display.template.php line 758. Is it somewhere else I should add it?In the index.template.php and the Boardindex.template.php there are no forms. In the org2_index.template.php I have tried to add the line in line 271. Still no login.

I can not just make a csv of the members table in tho old database, and upload it to the new one, to get my old members "on-board" again?

yeah, i tried that once... and will second Illori's comments that it is not a good idea... it's in fact a rotten one.

if you're bound and determined to run with the 'new' install, just dump the database with the data and upload it to the new one.

but... i wager your issue with the 'old' is simple... for instance, you said you corrected the login in display, but did you correct it in index.template? there are several login's floating about- for instance i had a heckuva time before i realized the SSI had a login i used that needed adjusting... or, you can side step all of than and install the login fix mod.

ouch, @kindred- yeah, i was assuming they're using the same URL and paths... otherwise, it'll be a mess...

@peterkroman: IF IF IF the URL and paths are the same, yes- you can dump the data (make a copy) from the loaded DB and populate the new DB with that data, and not miss a beat- but your paths have to be the SAME... I don't even know if repair settings is clever enough to straighten that out otherwise- one of the elders here will have to answer that for us...